1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and more particularly, to a photoelectric conversion apparatus including a circuit configured to detect a maximum value and a minimum value.
2. Description of the Related Art
An AF (Auto Focusing) sensor is known to use a photoelectric conversion apparatus configured to output a maximum value and a minimum value of signals output from an array of photoelectric conversion units. Japanese Patent Laid-Open No. 2000-180706 discloses an AF sensor having a signal processing apparatus that allows a reduction in noise.
There may be a need for a further improvement in accuracy of AF sensors. To meet this need, the AF sensor tends to have a greater number of pixels. However, in the technique disclosed in Japanese Patent Laid-Open No. 2000-180706, if the number of pixels is increased, the result is an increase in the number of MOS transistors connected to a common output line and an increase in current used to drive the common output line.
When a maximum value or a minimum value is detected, an error among pixels can occur due to a voltage drop caused by resistance of each MOS transistor connected to the common output line and a current that drives the common output line. More specifically, in a configuration disclosed in FIG. 1 of Japanese Patent Laid-Open No. 2000-180706, an image signal from each photoelectric conversion unit is output via a minimum-value-detection differential amplifier 11. The minimum-value-detection differential amplifier 11 is configured in the form of a voltage follower, and an output terminal thereof is connected to the common output line via a transistor 13 disposed between the differential amplifier and the common output line. When a signal is output from the minimum-value-detection differential amplifier 11 to the common output line, a voltage drop occurs via the transistor 13 disposed between the differential amplifier and the common output line. If there is a difference in characteristics among the transistors 13 due to a variation in a production process, a variation of the voltage drop occurs, which may produce an error. The error increases with increasing current that drives the common output line.